Hybridoma technology for the production of monoclonal antibodies, which was developed by Kohler and Milstein [Nature, 256, 495 (1975)], has recently come into frequent use. This technology has several marked features; for instance, antibodies of a single specificity to each antigenic determinant can be produced, and antibodies obtained against roughly purified specimens need no absorption procedure. Moreover, from the viewpoint of antibody production, the technology is advantageous in many aspects, for instance in that when hybridomas are grown, particularly in mammalian heat high-titer antibody specimens can be obtained as desired, in large amounts and with constant quality and good reproducibility. In this sense, the utility of the technology of obtaining monoclonal antibodies by use of hybridoma is rated high. The modes of utilization of monoclonal antibodies are not limited to antigen detection. For instance, they are used for the purification of trace components through the preparation of antibody columns [Nature, 285, 446 (1980)]. Furthermore, the use thereof as diagnostic reagents or therapeutic agents has been developed [European Journal of Immunology, 9, 94 (1979)].
It is known that human interferon (IEN) includes at least three antigenically different types, namely alpha, beta and gamma [Nature, 286, 110 (1980)]. It is also known that gamma-interferon (IFN-.gamma.) is produced mainly by T lymphocytes receiving stimulation from a mitogen or antigen, and IFN-.gamma. is also called immune interferon (I-IFN) [The Interferon System, Springer Publishing Co., New York, 1979]. It is anticipated that IFN-.gamma. is produced in living bodies as a result of various immune responses, and it is presumed that IFN-.gamma. plays an important role in immuno-regulation. IFN-.gamma. differs in antigenic characteristics and in inducer species from alpha-interferon (IFN-.alpha.) and beta-interferon (IFN-.beta.). It is further known that IFN-.gamma. is acid-labile and heat-labile [The Interferon System, Springer Publishing Co., New York, 1979].
IFNs are generally defined as antivirally active substances produced by living bodies. It has been proved that they have various other biological activities, and their antitumor activity is a focus of attention [Blood, 55, 711, (1980); ibid., 55, 875, (1980)]. For inhibiting tumor growth, two methods are conceivable. One is direct inhibition of tumor cell proliferation and the other is indirect inhibition of tumor growth via immune responses in hosts. The latter case possibly includes natural killer (NK) cell activation, macrophage activation and killer T cell activation, among others. In fact, it has been demonstrated that IFNs exert various immune-response-potentiating actions such as mentioned above in addition to direct actions [Biochemica et Biophysica Acta, 516, 231, (1978)]. Since IFN-.gamma. is by far higher in such various in vitro activities associated with antitumor effect and in vivo activities than IFN-.alpha. and IFN-.beta., its importance has been emphasized [Cellular Immunology, 49, 390, (1980)].
However, the IFN-.gamma.-potency that can be induced in vitro is generally low, few established cell lines are adequate enough as IFN-.gamma.-producing ones, and IFN-.gamma. purification is difficult due to its lability to heat and acids. For these and other reasons, the large-scale production and purification of IFN-.gamma. have been much delayed as compared with IFN-.alpha. and IFN-.beta..
Very recently, it was reported that natural IFN-.gamma. could be made singly [Proceedings of the National Academy of Science, 79, 1820, (1982)], but recovery of activity is very poor. A more effective purification method, therefore, has been eagerly waited for.
On the other hand, cloning of the human IFN-.gamma. gene has been reported, as well as production of an approximately 17 kilodalton molecular species composed of 146 amino acids, supposed to be IFN-.gamma. in Escherichia coli [Nature, 295, 503, (1982); Nucleic Acids Research, 10, 2487, (1982)]. However, natural product IFN-.gamma. reportedly includes various species having different molecular weights and the counterpart relationship among the molecular species is unknown.
The present inventors have obtained monoclonal antibodies which are able to distinguish various IFN-.gamma. species which is not only important for establishing the correspondency among molecular species but also provides a very powerful weapon for purifying natural IFN-.gamma. or IFN-.gamma. produced in Escherichia coli by using genetic engineering techniques. A very recent report describes the acquisition of a monoclonal antibody against natural IFN-.gamma. [Nature, 296, 258, (1982)]. When IFN-.gamma. comprises a plurality of molecular species, it is very important to obtain monoclonal antibodies to molecular species cloned by gene manipulation techniques.